Speaker assembly



Sept. 8, 1959 H. R. JOHNSON SPEAKER ASSEMBLY 4 Sheets-Sheet 2 Filed June14, 1956 INVENTOR JOHNSON FI/G. 2

HOWARD R Mm A ORNEY Sept. 8, 1959 H. R. JOHNSON 2,903,084

SPEAKER ASSEMBLY Filed June 14, 1956 4 Sheets-Sheet 3 in m IN VENTORHOWARD R. JOHNSON A 0' EY fig Sept. 8, 1959 Filed June 14, 1956 OQI OOI

H. R. JOHNSON SPEAKER ASSEMBLY O In m 9. 1 13 1| 1/ A I q: I I I I IWITHOUT TRANSDUCER WITH TRANSDUCER 4 Sheets-Sheet 4 INVENTOR UnitedStates Patent SPEAKER ASSEMBLY Howard R. Johnson, Collingswood, NJ.Application June 14, 1956, Serial No. 591,418 4 Claims. 01. 181-31) Thisinvention relates to speakers for radios and particularly, but notexclusively, to high fidelity sets. The principal object of theinvention is to provide a speaker assembly requiring considerably lessspace than is presently thought the minimum and yet to be able toreproduce accurately notes of low tones while extending the range ofhigh notes.

An important object of the invention is to add a transducer in front ofa radio speaker, touching or close to the cone, and confining a volumeof air between two parallel membranes in the path of sound waves fromthe speaker, thus greatly smoothing out the curve of the speaker asplotted between decibels and cycles per second. While this object is hadwith any type of speaker, it is most noticeable in the tweeter rangewhich is extended from about 10,000 cycles per second to 15,000 cycles,the peak of the curve extending just to the zero line and thuseliminating the characteristic crossing and recrossing into positivevalues that is found in most of the high fidelity tweeter speakers.

A further object of the invention is to apply a drumlike transducer to aspeaker having no cone, the voice coil being directly connected with oneof the two parallel membrane heads of the transducer, there preferablybeing a ventilating opening through the magnet so as to transmitrearwardly a certain amount of sound.

A further object of the invention is a method of increasing the purityof tone and the range in cycles of the speaker, which method includespassing the sound waves from a cone to the head of a transducer and backaround the speaker frame, passing out through a baifie having a numberof rather small openings, the holes preferably being at 90 apart andformed in part by coaxial semi-circles.

At the present time high fidelity sets reproduce with remarkableaccuracy the original sounds but to be able to do this the apparatus hasto be complicated and, most of all, the speaker cabinet is required tobe of huge size, including a tweeter, a woofer, and one or moreintermediate speakers. The present invention is concerned with greatlyreducing the size of the speaker cabinet by adding in front of theseveral speakers a dead air space bounded by a pair of spaced membranespreferably, though not necessarily, parallel. When such a transducer isplaced in the path of the sound waves from a speaker cone, there is anoticeable change in the sound waves and a definitely increasedfidelity, especially with low volume. The present invention permits theuse of much greater power without loss of accurate reproduction than canbe permitted with present [day apparatus. With a woofer using atransducer as small as a cube eighteen inches on each side overall, thesound may be taken below forty cycles per second, and a sound meter willindicate a very smooth curve extending from the lowest cycle to thehighest.

In the drawing:

Figure 1 is a horizontal cross section through a preferred form of thedevice.

Figure 2 is a front view largely broken away to show the woofer andtweeter in front elevation.

Figure 3 is a central section through the tweeter.

Figure 4 is a chart showing the frequency response curves with andwithout the transducer.

Figure 5 is a modified form of woofer.

The cabinet is shown as a 16 inch cube, the back 14 and the side panels15 and 16 being solid pieces of wood, preferably soft pine suitablyveneered. The front panel 12 has a central 8 inch circular opening 17and has four smaller openings 18, preferably spaced near each corner ofthe front panel 12 and consisting principally of two coaxialsemi-circular sides 19 and 20. The front panel, as usual, is entirelycovered by the customary grill cloth 21. The case or cabinet 10 is linedat top, bottom, both sides and back with a sheet of open cell vinylmaterial 27 having a thickness of at least one inch and preferably more.This lining, which is shown as 1 /2 inch thick, fits snugly between thefront corner bracing 28 and the rear corner bracing 2.9, the latterbeing triangular in cross section.

A circular transducer 30 fits snugly in the central space in the cabinetleaving four fairly large corner air spaces 31. The shell 32 of thetransducer may be of metal, pasteboard, plastic, or similar material andneed be only one eighth of an inch thick. This transducer uses the cone33 of the speaker as its forward head and there-' fore has only oneother head 35 of membrane material, preferably rayon cords imbedded inneoprene. The head 35 is made taut by the tensioning hoop 37 which ismoved axially by turning the tension screws 38 threaded into sleeves 39carried by the transducer shell 32 prefer-.

ably by screws 40 spaced either 60 or apart; The

gaged by hooks 42 carried by brackets 43 in which the screws 38 freelyturn. The shell 32 frictionally engages the thick walls of the lining 27and is therefore securely anchored to the cabinet.

A half inch by one inch closed cell vinyl gasket 44 is positionedbetween the shell 32 of the transducer and the peripheral edge 45 of thespeaker frame 46, usually having a pasteboard annulus 47 secured withinits flange. The speaker cone 33 is made fast to the edge 45 in usualfashion and is connected to the voice coil 50 within the magnet 51. Thecentral opening in the magnet casing has the usual fabric cover 52coaxial with the central opening 17 in the front panel 12 of thecabinet. The vibrations from the cone pass through the closed spacebounded by the dust cap 53, the cone 33, the transducer shell 32, andthe flat membrane 35 and are returned through the cone and the severalopenings 55 in the speaker frame and pass out through the fairly largeopening 17.

In Figure l the details of the tweeter 59 are omitted for clearness ofillustration. It is located in the upper right hand corner of thisfigure which is a horizontal section. The tweeter is better shown,however, in Figure 2 in its proper location in one of the four cornersof the cabinet and is shown in cross section in Figure 3 with atransducer 60 cylindrical in section and of an axial length givingbetter results where there is ample available space. In Fig. 2 thetransducer is of cross-section corresponding to the elliptical shape ofthe tweeter speaker cone and is between such cone and the front panel,discharging its sound through the small opening 18 immediately in front.

The transducer 60 in each case is quite small, having a tone may be hadby moving the cone very slightly away from the head. The tweeter 59 isof standard form and is either circular with 4 /2" diameter or it maycarry a 4" :by 6" loud speaker. The transducer for such a tweeter is 6"in diameter and 7" in length.

The chart, Figure 4, has a full line curve 68 showing the frequencyresponse plotted between decibels and cycles per second. It should benoted that this curve runs from 250 cycles to 10,000 cycles and is quiteirregular. Curve 69 represents the frequency response with thetransducer in place. Here the curve extends quite smoothly from 140cycles to 15,000 cycles and at no time does this curve pass above thezero line and into the positive values.

In Figure is shown a cross section through a woofer in which the conehas been omitted. The magnet 70 has the usual air passage 71 and thevoice coil 72 is connected as by a sleeve 73 of very light weightmaterial to the membrane 74 forming one head of the transducer 75; theother head, which is covered, being 76. The shell of the transducer asin the preferred form is surrounded by a lining of open vinyl materialat least an inch thick. There is an air space 77 between the speakerframe 78 and the head 74.

What I claim is:

1. A radio speaker assembly comprising a cabinet having a sheet of opencell vinyl compound at its rear, top, bottom, and both sides of thecabinet, a radio speaker frictionally engaging said sheet so as to besecurely anchored to the cabinet thereby and having a cone, a closedcell vinyl gasket engaging the periphery of the speaker cone, and a drumwith a membrane facing said cone and forming with the cone and the shellof the drum a dead air space circular in cross-section.

2. A speaker assembly comprising a cabinet having a back, top, bottom,and two sides all lined with -a sheet of open cell vinyl, also a frontpanel having a central opening; a woofer speaker and a tweeter speakerwithin the cabinet, each speaker having a cone, a two-headed drumtransducer positioned in front of each cone and each forming a dead airspace within the cabinet, and means within the side sheets of vinyl fortightening one head of one of the transducers.

3. The speaker assembly of claim 2 in which the shell of the wooferspeaker transducer is snugly engaged by the vinyl linings, and a ringgasket engaging one end of said shell, the cone of the woofer speaker,and the lining of the cabinet.

4. A radio speaker assembly comprising a cabinet having a sheet of opencell vinyl compound at its rear, top, bottom, and both sides of thecabinet, a radio speaker frietionally engaging said sheet so as to besecurely anchored to the cabinet by said sheet, a cone for the speaker,a two-headed drum transducer firictionally engaging said sheet andhaving a cylindrical shell of greater axial length than the axial lengthof the cone, the cone forming one of the two heads of the drumtransducer, the other head of the drum being positioned perpendicularlyto the axis of the drum, and means for tensioning said other head.

References Cited in the file of this patent OTHER REFERENCES Plastics(publication), vol. XV, Issue 155, pp. 9395, April 1950. (A copy in theScientific Libraly, US. Patent Oflice.)

